Glycoprotein hormones and free subunits are secreted by animal and human pituitaries in vivo and in vitro. Normal thyrotropic cells synthesize alpha subunit in excess of beta subunit, but the production of the latter is preferentially regulated by thyroid hormones. Pituitary tumors may secrete alpha subunits and TSH in an abnormal fashion and may be autonomous to normal regulatory factors. Heterogeneous forms of immunoreactive TSH and subunits have been identified, and certain forms of subunits have abnormal combining properties. Studies are in progress to further elucidate the mechanism of biosynthesis of glycoprotein hormones. BIBLIOGRAPHIC REFERENCES: Re, R.N., Kourides, I.A., Ridgway, E.C., Weintraub, B.D. and Maloof, F.: The effect of glucocorticoid administration on human pituitary secretion of thyrotropin and prolactin. J. Clin. Endocrinol. Metab. 41: 338-346, 1976. Kourides, I.A., Re, R.N., Weintraub, B.D., Ridgway, E.C. and Maloof, F.: Metabolic clearance and secretion rates of subunits of human thyrotropin. J. Clin. Invest. 59: 508-516, 1977.